1. Field of the Invention
The present invention relates to an ink jet print head used in an ink jet recording system for performing a recording operation to a recording medium by flying a small ink droplet, and an ink jet printing device using this head.
2. Related Background Art
There are a method utilizing an electrothermal converting element (heater) as a discharging energy generating element used to discharge an ink droplet and a method utilizing a piezoelectric element as this discharging energy generating element in an ink discharging method of an ink jet recording system widely generally used at present. In each of these methods, discharging of the ink droplet can be controlled by an electric signal. For example, in the principle of the ink droplet discharging method using the electrothermal converting element, ink in the vicinity of the electrothermal converting element is instantaneously boiled by giving the electric signal to the electrothermal converting element, and the ink droplet is discharged at high speed by growing a sudden bubble caused by a change in phase of the ink at this time. In contrast to this, in the principle of the discharging method of the ink droplet using the piezoelectric element, the piezoelectric element is displaced by giving the electric signal to the piezoelectric element and the ink droplet is discharged by a pressure at a time of this displacement. Here, with respect to merits in the former method, it is not necessary to arrange a large space for the discharging energy generating element, and the structure of an ink jet print head is simple and ink flow paths are easily integrated, etc. However, in this method, the air dissolved within the ink is eluted by heat generated from the electrothermal converting element and a residual bubble is caused within the ink jet print head. When this residual bubble is left as it is, the residual bubble has bad influences on discharging characteristics of the ink droplet and an image.
The influences of the residual bubble within the ink jet print head caused by the air dissolved within this ink on the ink droplet discharging characteristics and the image will next be explained in detail. The air is normally dissolved into the ink within the ink jet print head in a saturation state. When the electrothermal converting element is operated in this state, there is a case in which the air dissolved into the ink suddenly appears within the ink as a dissolved bubble having a diameter equal to or smaller than about 1 xcexcm in repetitions of adiabatic contraction of foaming and a sudden bubble by a change in phase of the ink. It is also known that such a bubble is again dissolved into the ink for a time determined from a bubble diameter, surface tension of the ink, a saturated vapor pressure of the air, etc. For example, if the bubble diameter is equal to smaller than 1 xcexcm, a time required for the dissolution is an order equal to smaller than 1 xcexcs. However, when plural electrothermal converting elements are continuously operated at high frequency, a plurality of such bubbles appear within the ink and are mutually collected and grown before these bubbles are again dissolved. It is known that a time required for the redissolution is greatly increased when the bubble diameter is increased. As a result, plural residual bubbles from several tens of xcexcm to several hundred xcexcm in diameter are stored within the ink jet print head. In such a case, no such residual bubbles are almost again dissolved into the ink so that these residual bubbles have a bad influence on discharging characteristics of the ink droplet. Namely, if an ink flowing path is blocked by the residual bubbles, the ink flowing path is not filled with sufficient ink so that a discharging defect is caused. Further, when a great residual bubble (about several hundred xcexcm in diameter) is caused within the ink jet print head and is accidentally communicated with the external air, the external air enters the ink flowing path so that a meniscus is broken. Therefore, the ink within the ink jet print head is sucked-up to an ink tank by a negative pressure for sucking-up the ink of the ink tank so that no ink is discharged from the ink flowing path in a certain case. As a most effective solving means for avoiding such a bad influence of the residual bubbles, there is a method for externally discharging the residual bubbles together with the ink from an ink discharge port by suction, pressurization, etc. before the residual bubbles are grown to such an extent that the residual bubbles have the above-described bad influence. This method is a method for performing so-called suction (pressurization) restoring processing. However, in this case, a consuming amount of the ink is greatly increased and throughput is naturally reduced if this method is executed during a printing operation. There is another method in which the air dissolved into the ink is discharged from the ink (deairing) by a certain method, and such ink is used in the ink jet print head. A most effective operating time of this solving method is about several tens of minutes from the deairing of the ink, and a device for deairing the ink is relatively large-sized so that usage of this technique is limited to a printing system, etc. on a large scale.
Therefore, in consideration of such a problem of the residual bubbles, in an ink jet print head described in Japanese Patent Application Laid-Open No. 10-146976, as shown in FIGS. 7A and 7B, plural projections 7 are arranged at a certain interval just above an ink supplying port 8 on the inner surface of a discharging port plate 5 so that growing of a bubble attached to the inner surface of the discharging port plate 5 is restrained. Further, a common ink flowing path portion common to electrothermal converting elements 1 as adjacent discharging energy generating elements 1 is arranged to stably supply ink so that supplying interruption of the ink caused by flowing a bubble 11 attached to an end tip of a projection 7 and grown to about xcfx86150 xcexcm in diameter into the ink flowing path is restrained.
However, in the above conventional examples, the bubble itself exists near the ink supplying port as it is. Therefore, when the ink is printed to an elongated recording medium as in banner printing, textile printing, etc. there is a case in which restoring processing must be intermediately performed. However, when a restoring operation is performed during printing of one sheet, a color tone is changed in this restoring portion and this change has a bad influence on printing quality. Therefore, it is not desirable to perform the restoring operation during the printing. Such a situation can be avoided by performing the restoring operation at any time every time the recording medium is changed. However, when the restoring operation is often performed, the throughput of a printed matter is reduced. Further, a problem exists in that a useless ink amount is increased.
In consideration of the above problems, an object of the present invention is to provide an ink jet print head for relaxing the bad influence of a bubble left within the ink jet print head on ink liquid discharge, and discharging a stable ink droplet with high reliability.
Another object of the present invention is to provide an ink jet printing device having an excellent throughput and reducing an ink consuming amount by controlling a residual bubble and further reducing the number of restoring times.
To achieve the above objects, in the present invention, an ink flow is made near a through port of a substrate of an ink jet print head by a hydrodynamic action of ink so that a bubble attached to a wall face of a common liquid chamber is easily separated therefrom or the bubble is not easily attached to this wall face. In the construction of the present invention, an ink jet print head comprises plural electrothermal converting elements for generating energy used to discharge an ink droplet; plural ink discharge ports arranged above the electrothermal converting elements and discharging the ink droplet; plural ink flowing paths respectively communicated with the plural ink discharge ports and internally including the electrothermal converting elements; a substrate for arranging the plural electrothermal converting elements in a columnar shape and having an ink supplying port constructed by a through port which is connected with the ink flowing paths and extends along an arranging direction of the electrothermal converting elements; and a discharging port plate having the ink discharge ports; the ink jet print head being constructed such that the ink flowing paths are formed between the substrate and the discharging port plate by junctioning the discharging port plate onto the substrate; and the ink jet print head further comprising fluid resisting means of the ink flowing paths in which a side of the ink supplying port is opened in the vicinity of a communication portion of the ink flowing paths in an ink supplying port projecting area of the discharging port plate.
In accordance with the ink jet print head having the above construction of the present invention, a speed component in a direction of the common liquid chamber can be given to the ink flow parallel to the discharging port plate near the ink supplying port at an ink discharging time. Therefore, the bad influence of a bubble left within the ink jet print head on ink liquid discharge is relaxed. Accordingly, it is possible to provide an ink jet print head in which an ink droplet is stably discharged with high reliability. It is also possible to provide an ink jet printing device in which throughput is excellent and an ink consuming amount is reduced by further reducing the number of restoring times.